Unless I'm using a Belgian yeast, I usually just use a bung and bubbler. And I add Fermcap-S to keep the krausen in check, if it looks like it's getting out of hand.

I use the cheapest vodka I can find in the airlock. A small amount of vodka in 5 gallons of beer can easily go undetected. But, so far, I've only seen vodka sucked back into the carboy once. I guess I don't crash it especially fast. I set ambient down near freezing. And usually the beer takes a while to get there. So, the vacuum effect is probably negligible because of that. And the yeast still drops out at that lower temp in short order.

I dip a new zip lock bag (I keep them in the brewery all the time to hold my measured hop additions) in Star San and stick it over the top of the carboy. I, too, have sucked Star San back into the carboy.

Try switching your 3-piece airlock to an S-shaped airlock. Put just a tiny bit of starsan or vodka (or even tap water for that matter) in it. When you cold crash, the pressure difference will not suck the liquid all the way through into the carboy. Just be sure to use a small amount to block any oxidation from occurring.

_________________"A bad man is a good man's job, while a good man is a bad man's teacher."

Try switching your 3-piece airlock to an S-shaped airlock. Put just a tiny bit of starsan or vodka (or even tap water for that matter) in it. When you cold crash, the pressure difference will not suck the liquid all the way through into the carboy. Just be sure to use a small amount to block any oxidation from occurring.

Yeah, that's probably why I haven't had any significant problems. The S shaped airlock mostly just lets some air bubble back into they carboy.

Makes me wonder how much air it sucks back in, though. Good thing there's a blanket of CO2 over the top of the beer, I guess.

Try switching your 3-piece airlock to an S-shaped airlock. Put just a tiny bit of starsan or vodka (or even tap water for that matter) in it. When you cold crash, the pressure difference will not suck the liquid all the way through into the carboy. Just be sure to use a small amount to block any oxidation from occurring.

Yeah, that's probably why I haven't had any significant problems. The S shaped airlock mostly just lets some air bubble back into they carboy.

Makes me wonder how much air it sucks back in, though. Good thing there's a blanket of CO2 over the top of the beer, I guess.

Regardless of whether you use an s-bubbler, foil, or silicone bung when the warm air in the headspace cools and contracts you will suck in the same volume of air, making differences in "oxidation" meaningless. Except possibly the silicone bung .... you might create an air tight seal than leads to negative pressure in the headspace that then equilibrates with CO2 from the beer or allows air in when you open to transfer but with shorter contact time there might be a real (minor) difference.

When I use a blow off tube, I don't bury the opening in star san just point it downward into a bucket. Bacteria and yeast won't climb up the tube, and the generation of CO2 in the beer will keep the oxygen out. Then if I have a decrease in temp, nothing to suck back in.

When I use a blow off tube, I don't bury the opening in star san just point it downward into a bucket. Bacteria and yeast won't climb up the tube, and the generation of CO2 in the beer will keep the oxygen out. Then if I have a decrease in temp, nothing to suck back in.

The only down side I see is fruit flies. .... .... I hate fruit flies

You could put mesh over the down end of your tube to keep them from crawling in... If you are concerned about contraction of headspace pulling air back into the carboy, I suppose you could fill a balloon with CO2 and attach that to the end of a blow off tube so that anything it pulls in is CO2....

_________________SpiderwranglerPFC, Arachnid Deployment Division

In the cellar: In the fermentor: Belgian CiderIn the works: Wooden Cider